MONDAY, Nov. 28, 2016 (HealthDay News) -- Women who think they're too old to worry about mammograms may want to reconsider the age at which their breast cancer screening years are behind them, a new study suggests.

Based on an analysis of nearly 7 million mammograms over a seven-year period, "the benefit continues with increasing age up until 90," said study author Dr. Cindy Lee. She is an assistant professor in residence at the University of California, San Francisco.

The question of when to stop having mammograms has been widely debated. In 2009, the U.S. Preventive Services Task Force issued new guidelines, saying there wasn't enough evidence to assess the balance of benefits and harms of screening mammography in women aged 75 and older.

Lee and her colleagues looked at patient age, mammogram results, recall rates for more testing, biopsy referrals and biopsy results. The investigators also looked at the percentage of breast cancers found when a biopsy was recommended or performed. Ideally, Lee explained, screening should result in a higher cancer detection rate and a low recall rate.

In the analysis, which included data from 39 states from 2008 through 2014, nearly four breast cancers were found for every 1,000 patients screened. The recall rate was 10 percent.

"We are finding more cancers with increasing age," Lee said, which makes sense because the risk rises with age. "We are doing better at catching them," she said. And, "we have decreased the recall rate. We are calling back fewer women for additional testing, but are finding more cancers."

The study authors concluded that "there is no clear age cut-off point" to determine when to stop screening.

The study findings suggest that the decision to screen may depend on a woman's personal choice and health status. Older women with 10 years of life expectancy, for instance, might choose to continue screening, Lee said.

The study was to be presented Monday at the Radiological Society of North America annual meeting, in Chicago. Studies presented at medical meetings are viewed as preliminary until they are published in a peer-reviewed journal.

Robert Smith, vice president of screening for the American Cancer Society, said the study findings show that mammograms are still worthwhile after the age of 70.

"Breast cancer incidence and mortality increase as women age, and roughly 30 percent of breast cancer deaths each year occur in women who were diagnosed after the age of 70," he said.

"Many of these deaths are avoidable, as Lee and colleagues demonstrate in this new report, since mammography screening performs increasingly well as women get older. While incidence is high, the disease is slower growing and density is lower, providing improved opportunity for early detection," Smith explained.

"Their [the researchers'] conclusion that these data provide no support for a particular age to stop screening is consistent with the American Cancer Society breast cancer screening guideline, which states that the decision to continue screening should be based on individual patient values, [co-existing] conditions, overall health status and estimated longevity," he noted.

But Smith added a caveat.

"While it is the case that too many older women stop screening prematurely, it also is the case that too many women with serious chronic conditions and few remaining years to live continue to be screened for breast cancer," he said.

Such women aren't likely to benefit from continued breast cancer screening. Smith said. "And the detection and treatment of breast cancer in a woman with limited longevity may also further diminish the quality of life of her remaining years," he said.

"Breast cancer screening should continue as long as there will be value from early detection, and should cease when the potential for benefit no longer exists," Smith added.

More information

To learn more about breast cancer screening for older women, visit Breastcancer.org.